Physics Module 2

Front 1

Advantages of photocells:
- They're robust and don't need much maintainance
- They don't need any fuel or long power cables
- They don't cause pollution or contribute to climate change
- They use a renewable enrgy source
The only disadvantage is that they don't provide electricity when it is dark.

Back 1

How photocells work:
A photocell contains two pieces of SILICON joined together to make a P-N JUNCTION. An electric field is created between the two pieces.
- One pice has an impurity added to produce an EXCESS of FREE ELECTRONS- N-TYPE SILICON.
The other piece has a different impurity added to produce an ABSENCE of free electrons- P-TYPE SILICON.
The electrons are attracted to the P-type silicon so move over. Then they try to return but can't because of the P-N Junction so leaves via an external circuit. This charges the battery, which in turn gives you the energy.
(Sunlight contains energy packets called PHOTONS. Photons cause free electrons to move producing an electric current.

Front 2

Solar heating:
A house that uses PASSIVE SOLAR HEATING makes use of direct sunlight. It has large windows facing the sun (South) and small windows facing north.
-during the DAY, energy from the sun warms the walls and floors.
- During the NIGHT, the walls and floors radiate energy back into the room.
Curved solar reflectors FOCUS energy from the sun.

Back 2

Solar heating:
SOLAR REFLECTORS are moved by a computer to make sure they're always facing the sun.
The temperature inside a greenhouse is higher than on the outside.
- The sun is very hot and produces radiation with a short wavelength. This radiation passes through glass and is absorbed by plants and soil.
- The plants and soil aren't as hot and re-radiate energy with a longer wavelength (Infrared).
- This radiation isn't able to pass through glass and is reflected back into the greenhouse.

Front 3

Wind energy:
Moving air has kinetic energy which is transferred into electricity by a wind turbine.
Wind farms don't contribute to global warming, nor do they pollute the atmosphere.
They don't work if there isn't any wind, or if the wind speed is too great. Furthermore, they can be noisy and impact on the countryside.

Back 3

Generators:
The current from a DYNAMO can be increased by:
- Using a stronger magnet
- Increasing the number of turns on the coil
- Rotating the magnet faster.
The voltage and frequency from a dynamo can be displayed on an OSCILLOSCOPE.
The formula to work out the frequency is:
FREQUENCY (iN HERTZ, Hz) = 1/ PERIOD (IN SECS, s)
The generator at a power station works like a dynamo. A simple generator consists of a coil of wire rotating between the poles of a magnet to produce a current in the coil. In a power station, FUEL is burned to heat water to produce steam. Steam a high pressure turns a turbine which then drives a generator.

Front 4

Distributing Electricity:
The national grid distributes electricity around the counrty at HIGH VOLTAGES. This means that:
- There's less energy loss
- The distribution costs are lower
- Electricity prices are cheaper
Some transformers in the national grid increase (Step up) voltages, others decrease (Step down) voltages.
Electricity in the UK is generated with a frequency of 50Hz.
When a current passes through a wire, the wire gets hotter. The greater the current, the hotter the wire becomes.
When a transfromer increases the voltage, the current decreases. There's less heating effect and less energy is lost to the environment.
EFFICIENCY= OUTPUT/INPUT
FUEL ENERGY INPUT= WASTE ENERGY OUTPUT + ELECTRICAL ENERGY OUTPUT

Back 4

Fuels:
A fuel burns air to release energy in the form of heat.
BIOMASS can be burned. It can be FERMENTED to produce METHANE, which is then burned.
NUCLEAR FUELS don't burn. In a nuclear reactor, uranium atoms split and release lots of energy as heat. Nuclear reactions in power stations have to be controlled to avoid an explosion.
Fossil fuels are NON-RENEWABLE and produce carbon dioxide, a greenhouse gas that contributes to climate change.
Biomass energy sources are RENEWABLE, but still produce carbon dioxide when used as a fuel.

Front 5

Power:
Power is a measure of the rate at which energy is used. The unit is the WATT. (W)
POWER = VOLTAGE X CURRENT
ELECTRICAL CONSUMPTION is the amount of energy that's been used. The unit is the KILOWATT HOUR (kWh)
ENERGY USED = POWER X TIME
COST OF ELECTRICITY USED = ENERGY USED X COST PER kWh
Electricity is cheaper at night when not as much is needed but still has to be produced.

Back 5

Nuclear Power:
Radiation from nuclear waste causes ionisation, which causes a change in the structure of any atom exposed to the radiation.
The cells of our bodies are made up of many different atoms. DNA is an important chemical in a cell and can be changed when it's exposed to radiation. The cell behaves differently to normal and this is called a mutation. One effect of a mutation is for a cell to divide in an uncontrolled way. This can lead to cancer.
Waste from a nuclear reactor can remain radioactive for thousands of years.
Plutonium, one of the waste products, can be used to make nuclear weapons. Nuclear bombs destroy everything in a very large area and make that area unusuable for a long time.

Front 6

Nuclear radiation:
Most background radiation is naturally occuring.
Alpha, Beta and Gamma radiations come from the nucleus of an atom.
Alpha radiation causes the most ionisation and Gamma radiation the least. Ionisation produces charged particles.
Ionisation involes gaining or losing electrons:
-When the atom gains them, it becomes negatively charged.
- When the atom loses them, it becomes positively charged.

Back 6

Uses of radioactivity:
ALPHA RADIATION is used in SMOKE ALARMS.
BETA or GAMMA sources are used in rolling mills to control thickness.
GAMMA sources are injected into the body as tracers.

Front 7

Radioactive waste:
Some radioactive waste can be reprocessed into new, radioactive material.
Radioactive waste must be stored SAFELY because it can remain radioactive for thousands of years. It must be stored where it can't leak into natural underground water supplies and then into lakes and rivers.
Radioactive waste isn't suitable for making nuclear bombs, but it could be used by terrorists to contaminate water supplies or areas of land.

Back 7

Magnetic fields:
The magnetic field around a coil of wire is similar to the field around a bar magnet.
A magnet shouldn't be broguht close to a TV or computer screen because it causes the electron beam in the tube to change direction. The beam strikes the wrong part of the screenm giving a distorted picture.
When a coil of wire moves inside a magnet, a current is produced in the coil. This is the principle of the dynamo.
Within the core of the Earth, the solid inner cores moves with the liquid outer core. Electric currents are produced that create the Earth's magnetic field.

Front 8

Origin of the moon:
When the solar system was formed, there was probably more planets than today.
Scientists believe that there was another planet in the same orbit as Earth.
- The two planets collided and were both almost totally destroyed.
- Iron became concentrated at the core of the new Earth, less dense rocks start to orbit.
-These rocks clumped together to form the moon.
- The Earth and the moon were rotating much faster than they are now = The moon caused the speed of rotation to slow down.
The core of the moon doesn't contain Iron. This suggests that the debris came from the mantle. The iron from the core of the other planet fused with the iron from the core of 'old' Earth.

Back 8

Cosmic rays:
Cosmic rays are streams of charged particles originating from the sun and other bodies in space.
- They travel very quickly and have lots of energy.
- They interact with the Earth's magnetic field as they spiral around field lines concentrating at the poles.
-They're the cause of Auroras = Patterns of light seen in the sky at high latitudes.

Front 9

Solar effects:
The energy from a solar flare is equivalent to that from a million hydrogen bombs.
Large numbers of charged particles are emitted at very high speeds. These produce magnetic fields that interact with the Earth's magentic field.
Although only a small fractionof the energy from solar flares reaches Earth, it's enough to interfere with radio and microwave signals and affect power distribution through the national grid.

Back 9

Solar system: The universe:
The Earth is one of the planets in our solar system orbiting the sun.
In Aug 06, scientists decidedthat pluto shouldn't be considered a planet because of it's size and orbital shape.
Comets have ELLIPTICAL orbits. They pass inside the orbit of Mercury and out beyond the orbit of pluto.
A METEOR is made from grains of dust that burn up as they pass through the Earth's atmosphere. They heat the air around them which glows, and the streak of light seen is called a shooting star.
Black holes are formed where large stars used to be. You can't see a black hole because light can't escape from it.
Moons orbit planets and planets orbit stars because CENTRIPETAL force acts on them.
-Centripetal force acts towards the centre of the circular orbit.
- GRAVITATIONAL ATTRACTION is the source of the centripetal force.

Front 10

Exploration:
Unmanned spacecraft (PROBES) have explored the surface of the moon and mars. They can go to places where humans can't survive.
The hubble spacecraft telescope orbits the Earth collecting information from distant galaxies.
The moon is the only body in space visited by humans. Astronauts wear normal clothing in pressurised spacecraft, but outside they need to wear special spacesuits.
- A dark visor stops an astronaut being blinded.
-the suit is pressurised and has an oxygen supply for breathing.
- The surface of the suit facing towards the sun can be up to 120 degres.
-The surface of the suit away from the sun can be as cold as -160 degrees.
When travelling in space, astronauts experience lower gravitational forces than on the Earth.

Back 10

Light years:
Distances in space are measured in light years.
Light travels at 300,000 km/s.
- Light from the sun takes about 8 minutes to reach us.
-Light from the nearest star (Proxima Centauri) takes 4.22 years

Front 11

Asteroids:
Asteroids are miny planets or planetoids orbiting the sun in a 'belt' between mars and jupiter. They're large rocks that were left over from the formation of the solar system.
Geologists have examined evidence to support the theory that asteroids have collided with the Earth.
-Near to a crater thought to have resulted from an asteroid impact, they found quantities of the metal Iridium= a metal not normally found in the earth's crust but common in meteorites.
-Many fossils are found below the layer of iridium, but few fossils are found above it.
- Tsunamis have disturbed the fossil layers, carrying some fossil fragments up to 300km in land.
All bodies in space, including planets, were formed when clouds of dust and gas collapsed together due to gravitational forces of attraction.

Back 11

Asteroids continued:
The mass of an object determines it gravitational force. asteroids have relatively low masses compared to the mass of Jupiter. Jupiter's GF prevents asteroids from joining together to form another planet, so they remain in a 'belt' as they orbit the sun.
65 million years ago, an asteroid with a diameter of 10km struck the Earth. Dust from the collision passed into the atmosphere, blocking sunlight and lowering temperatures. Photosynthesis couldn't take place and herbivorous dinosaurs couldn't feed. This ultimately led to the extinction of all dinosaurs.


Comets:
Compared to the near circular orbits of the planets, the orbit of a comet is very ELLIPTICAL.
Most comets pass inside the orbit of Mercury and well beyond the orbit of pluto.
As the comet passes close to the sun, the ice melts. Solar winds blow the dust into the comet's tail so the tail always points away from the sun.
The speed of a comet increases as it approaches the sun and decreases as it gets further away. This is

Front 12

NEO's:
Scientists are constantly monitoring and plotting the paths of comets and other Near-Earth-Objects.
If a NEO was on a collision course with the Earth, one option would be to launch a rocket filled with explosives. This could alter the course enough to miss earth.
If a NEO did hit Earth, the result could be the end of life as we know it.

Back 12

The big bang: The universe:
Almost all of the galaxies in the Universe are moving away from each other. The furthest galaxies are moving fastest. The universe is expanding all the time.
Microwave signals are constantly reaching Earth from all parts of the universe.
When a source of light is moving away from an observer, it's wavelength appears to increase. This shifts light towards the red end of the visible spectrum.- RED SHIFT.
When scientists look at light from the sun, there's a pattern of lines across the spectrum. This pattern moves towards the red end of the spectrum when they look at light from distant stars. The faster the star is travelling, the greater the red shift.
Scientists can use information from red shift to work out the age of the universe.

Front 13

Nuclear Power Dis/advantages:
Advantages:
- Fossil fuel reserves aren't being used
- There's no atmospheric pollution
- No carbon dioxide is produced so no global warming effects.
Disadvantages:
- Nuclear power stations have high maintainence costs, decommissioning costs and produce quantities of radioactive waste
- There's a risk of a major accident similar to the one at Chernobyl.

Back 13

Stars:
A medium sized star, like our sun, becomes a RED GIANT: the core contracts, the outer part expands and cools, and it changes colour from yellow to red. During this phase, gas shells, called PLANETARY NEBULA, are thrown out.
The core becomes a WHITE DWARF shining vey brightly, but eventually cools to become a BLACK DWARF.
Large stars become RED SUPERGIANTS as the core contracts and the outer part expands. The core suddenly collapses to form a NEUTRON STAR and there's an explosion called a SUPERNOVA. Remants from a supernova can merge to form a NEW STAR. The dense core of the neutron star continues to collapse until it becomes so dense it forms a BLACK HOLE.
The swirling cloud of gas and dust id a NEBULA. Nebula clouds are pulled together by gravity into a spinning ball of gas, which starts to get hot and glow.
The PROTOSTAR is shining but can't be seen because of the dust cloud. Gravity causes the star to become smaller, hotter and brighter.

Front 14

Stars 2

Back 14

After millions of years, the core temperature is hot enough for NUCLEAR FUSION to take place. As hydrogen nuclei join together to form helium nuclei, energy is released. The star continues to shine while there's enough hydrogen.
Small stars shine for longer than large stars because although they have less hydrogen, they use it up at a slower rate.
What happens at the end of a stars life depends on it's size.